Reactive adsorbents, examples of which are primarily focused on activated, impregnated carbon, remove toxic chemicals from the gas streams via reactions between the reactive impregnants and the target chemical. Activated carbon possesses a high porosity but is relative inert and therefore not able to appreciably facilitate reactions necessary to remove toxic chemicals, such as for example sulfur dioxide (SO2) and hydrogen cyanide (HCN). As a result, the activated carbon is impregnated with metal species, such as for example oxides, carbonates and hydroxides of metals that include copper and zinc, in order to facilitate the reactions. Although effective, activated, impregnated carbon is not without its drawbacks. As many reactions of interest are stoichiometric, the capacity of the activated, impregnated carbon is limited to the impregnant loading, which is often on the order of 6-10% by weight. In addition, the carbon substrate is flammable, presenting potential risks in applications employing large volumes of media, or when employed in reducing environments.
Zirconium hydroxide is a commercially available product that includes bridging oxygen and terminal hydroxyl groups. Although referred to as zirconium hydroxide, the material is in reality an oxy-hydroxide, as both ≡Zr—O—Zr≡ (bridging oxygen) and ≡Zr—OH (terminal hydroxyl) groups are present. Zirconium oxy-hydroxide is employed in a number of applications that include for example catalysis and ceramics. In these applications, the resulting catalyst or ceramic is fired at an elevated temperature, such as for example greater than 400° C., to yield the corresponding oxide.
Zirconium oxy-hydroxide in its as-received form was recently discovered to be effective in the removal of acid gases, such as for example sulfur dioxide (Peterson et al., Ind. Eng. Chem. Res. 48 (2009) 1694) and chlorine gases (Peterson and Rossin, Ind. Eng. Chem. Res. 51 (2012) 2675). As demonstrated by Peterson and Rossin (2012), only the terminal hydroxyl groups are reactive; i.e. able to contribute to the removal of chlorine gases.